Variable valve lift systems are known in the engine arts. See, for example, the systems disclosed in U.S. Pat. No. 6,668,779 and US Patent Application Publication No. 2008/0072855 published Mar. 27, 2008, the disclosures of which are both expressly incorporated herein by reference. Such systems typically incorporate a two-step roller finger follower to selectively transmit motion of either a high-lift cam lobe or a low-lift cam lobe of the engine's camshaft to an intake valve.
Valve deactivation systems for selectively activating and deactivating valves are also known. See, for example, U.S. Pat. No. 6,321,704 that discloses a deactivation hydraulic lash adjuster, and U.S. Pat. No. 7,093,572 that discloses a deactivation roller finger follower, the disclosures of which are both expressly incorporated herein by reference. Each of these deactivation systems prevents the rotary motion of a camshaft lobe from being translated into reciprocal motion of the associated valve stem by absorbing the equivalent motion within itself (“lost motion”). Thus the valve is “deactivated” and prevented from opening on schedule.
Customers' expectations of better engine performance and vehicle drivability, ever more stringent governmental regulations regarding engine emissions, and a mutual desire for higher fuel economy are increasingly at odds. Compromises inherent with fixed valve lift and event timing in conventional valvetrains have prompted engine designers to consider variable valve lift systems for more flexible air flow control optimized for each engine load and speed condition, and some variable valve lift systems have now been introduced on production engines. However, addressing critical engineering challenges concerning turbulence (swirl or tumble) enhancement in variable valve lift engines currently requires combustion chamber masking.
Engine combustion strategies in prior variable valve lift systems allow the intake valve to have discrete operational states known as high-lift and low-lift. In the high-lift operational state, the intake valve is allowed to reach a maximum open position, while in the low-lift operational state, the intake valve is only allowed to reach an open position intermediate of the closed and maximum open positions. However, variable valve lift mechanisms on dual intake valve engines have thus far been limited to providing the same lift on both intake valves of each cylinder, which cannot provide any in-cylinder air flow turbulence enhancement.
What is needed in the art is an internal combustion engine variable valve lift system wherein in-cylinder turbulence is enhanced during variable valve lift operation. Therefore, it is a principal object of the present invention to provide increased in-cylinder turbulence during variable valve lift operation of an internal combustion engine.